Asymmetric Catalysis Applications of (1R,2R)-trans-1,2-Diaminocyclohexane Derivatives Functionalized SBA-15 Mesoporous Silica
Date Issued
2016
Date
2016
Author(s)
Sun, Yan-Ru
Abstract
In this work, (1R,2R)-trans-1,2-diaminocyclohexane was grafted on mesoporous SBA-15 through either thio-ene addition or by substitution to generate a enantio-selective primary-tertiary or secondary-tertiary amine catalyst, respectively. These chiral selective catalysts were characterized by NMR, X-ray diffraction, N2 adsorption-desorption isotherm, and thermogravimetric analysis. These two enantio-selective catalysts were tested in asymmetric aldol reaction with p-nitrobenzaldehyde and cyclohexanone. The catalytic activities were also compared with the homogeneous one. The effect of using benzaldehyde derivatives with different substituents in the aldol reactions was examined and the possible transition states were also proposed. The experimental results demonstrated that a higher conversion up to 96% and higher stereo-selectivities were obtained in the presence of water over immobilized primary-tertiary amine catalyst than the 50% conversion over the secondary-tertiary amine catalyst. Hence, the primary-tertiary amine catalyst was the focus in this thesis for studying the effect of different parameters, including the protic and aprotic solvents, amount of water used as the solvent, and acid additives, alternation of stereo-selecticity with catalytic TFA under neat condition. The phenomenon of alternation was also examined by recycling test. In the last part, the effect of various substituents on benzaldehyde of different electron-withdrawing/donating strengths and sizes on the transition state and distribution of products in catalytic asymmetric aldol reaction over SBA-15 immobilized primary-tertiary amine catalyst are discussed. Different ketones as another reactant were also investigated to extend the application of this catalyst.
Subjects
direct aldol reaction
Organocatalysis
SBA-15
mesoporous silica
heterogeneous catalysis
asymmetric addition
SDGs
Type
thesis
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